The addition of RHNs to the SM particle content has nontrivial implications for the chemical transport in the primordial plasma in the early Universe.
Similar to weak sphaleron processes, which can wash in a baryon asymmetry in the presence of a primordial lepton asymmetry, RHN processes can wash in a \(B\!-\!L\)  asymmetry in the presence of primordial input charges.
This observation is the basis for the mechanism of wash-in leptogenesis, which we introduced in Ref. [1]} and which generalizes standard thermal leptogenesis to situations featuring a nontrivial chemical background induced by new \(CP\) -violating dynamics at higher temperatures.
In scenarios of wash-in leptogenesis, the energy scales of \(CP\)  and \(B\!-\!L\)  violation are hence separated from each other, which offers a wealth of opportunities for model building.
The RHN sector is no longer burdened with the requirement of sufficiently large \(CP\)  violation, and \(CP\)  violation in general no longer has to be tied to the generation of \(B\!-\!L\) .
Instead, it suffices if a dynamical \(CP\) -violating process at high energies, which may be referred to as chargegenesis, results in any of the conserved global charges that are present in the SM thermal bath at high temperatures.
In the extreme case of temperatures in the range \(T \sim 10^{13\cdots 15}\,\textrm {GeV}\) , this means that chargegenesis simply needs to produce a subset of the in total 15 available conserved charges,
\(q_e \,,\quad q_{2 B_1 - B_2 - B_3} \,,\quad q_{u-d} \,,\quad q_{d-s} \,,\quad q_{B_1 - B_2} \,,\quad q_\mu \,,\quad q_{u-c} \,,\quad q_\tau \,,\quad q_{d-b} \,,\quad q_B \,,\quad q_u \,.\) 
